In electrical equipment, which is insulated with a gas other than air, it is sometimes desirable to seal the gas within the device with a fused, inorganic seal. The problem is comparatively easy when the device is housed within a metallic tank, which can be welded, or brazed closed, and electrical connections with the interior parts made through bushings, which can be solder-sealed, or brazed into place. However, when it is desired to seal the device within a porcelain tube, for example, with metallic ends, the problem is then somewhat more difficult, especially when relatively high internal gas pressures are encountered.
In U.S. Pat. No. 3,163,736, issued Dec. 29, 1964, entitled "High-Voltage Gas-Type Circuit Interrupter," to J. J. Mikos et al, there is shown a method for making such a hermetic seal. However, the Mikos et al Patent relates to an outdoor device, and excess diameter is not a problem. For use in metal-clad switchgear, where space is at a premium, it is desirable to find a very compact sealing construction, and one which will maintain its hermetic sealing gas-tight condition over long operational periods of time.
In a gas-type puffer-type circuit-interrupter construction, such as set forth in U.S. patent application filed May 13, 1974, Ser. No. 469,586, by Stanislaw A. Milianowicz, entitled "Improved Puffer-Type Gas Circuit-Interrupter", there is illustrated and described a sealed-casing circuit-interrupter tube formed of porcelain, and having separable contact structure disposed therewithin. The porcelain casing is partially filled with a highly-efficient arc-extinguishing gas, such as sulfurhexafluoride (SF.sub.6) gas, for example. The pressure, internally of such an interrupter-casing construction, may, for example, be several atmospheres, for instance 70 p.s.i. During arcing conditions, this internal pressure may be increased considerably by the heat of the arc, and it is desirable to provide an end metallic closure plate member, which will be fixedly maintained in place, and yet will provide a hermetic gas-tight seal to the tubular insulating porcelain-casing structure to maintain the internal gas pressure therein without leakage occurring, which would, of course, permit the extinguishing gas, such as SF.sub.6 gas, for example, to escape to the surrounding atmosphere. According to accepted definitions, any seal which is air-tight is a "hermetic seal." However, in this disclosure, the term "hermetic seal" will be limited to include only fusion seals, such as glass-to-metal, solder seals, and brazed or welded joints.